1. Field of the Invention
The present invention relates to a rolled sheet support mechanism for pivotally supporting a rolled sheet, and a printer having the rolled sheet support mechanism.
2. Description of the Related Art
Currently, there are provided many thermal printers of various types, for performing printing by pressing a heated thermal head to a special recording sheet, which is to be discolored when being applied with heat. In particular, without using toner, ink, or the like, smooth character printing and colorful graphic printing can be performed, so the thermal printer is suitably used for printing of various labels, receipts, tickets, or the like.
Meanwhile, the recording sheet used for the various printers represented by the thermal printer is normally used while being wound around a cylindrical core tube to be formed into a rolled sheet. In general, the rolled sheet is mounted by one of two types of methods, one of which is of a drop-in type in which the rolled sheet is dropped in an accommodation space, and the other of which is of a pivot support type in which the core tube is pivotally supported (supported so as to freely rotate).
Of those, as one of the pivot support types, there is known a support structure for a rolled sheet, capable of rotatably supporting the rolled sheet and easily performing a replacement operation of the rolled sheet (see, for example, JP 2003-171037 A). The support structure for the rolled sheet includes a pair of support members each biased by an elastic member such as a coil spring toward an inside of a rolled paper container in which the rolled sheet is accommodated. The pair of support members each have, at an end thereof, a tapered tip portion to be fitted into a hollow hole of the rolled sheet. That is, the pair of support members can support the rolled sheet while pressing the rolled sheet by fitting the tip portions into the hollow hole from both sides thereof. That is, outer surfaces of the tip portions each formed into the tapered shape abut on inner edges of the hollow hole of the rolled sheet, thereby making it possible to retain the rolled sheet while pressing the rolled sheet from the both sides thereof. In this case, a biasing force of the elastic member is adjusted such that the rolled sheet is rotatable.
Further, the support members are merely biased by the elastic members. Therefore, receiving a force in a reverse direction with respect to a biasing direction, the support members move in the direction thereof, thereby allowing the rolled sheet to be attached.
According to the support structure for a rolled sheet, the replacement can be performed by a simple operation of only putting in or pulling out the rolled sheet into or from the rolled sheet accommodating portion. Further, the pair of the support members retain the rolled sheet by pressing the rolled sheet from the both sides of the hollow hole, so the rolled sheet can be pivotally supported with reliability.
However, there still remain the following problems with the conventional support structure for a rolled sheet described above.
That is, since the above-mentioned support structure for a rolled sheet is structured such that the pair of support members are pressed to the both sides of the hollow hole with the biasing force by the elastic members to support the rolled sheet by sandwiching the rolled sheet from the both sides thereof, a pressing force (biasing force) for sandwiching the rolled sheet is required to be set to a relatively large value. This is because, if the pressing force is small, there is a risk in that, when the rolled sheet rotates, the support members are detached due to vibration or the like, thereby causing the rolled sheet to fall off. In particular, the unused rolled sheet which has been just replaced is heavy, thus tending to fall off. Accordingly, in order to enable reliable supporting of even the unused rolled sheet, the pressing force is required to be adjusted to a large value in advance.
On the other hand, when the rolled sheet is attached, the pair of support members are required to be moved with a force standing against the biasing force of the elastic member so as to be spaced apart from each other in a lateral direction. However, when the pressing force is adjusted to the large value as described above, it is required to apply a force to the rolled sheet such that a force stronger than the pressing force is applied to the support members at the time of attachment of the rolled sheet. As a result, mountability of the rolled sheet is low and a replacement operation takes time and effort. Further, during the replacement, the support member continuously abuts on the side surface of the rolled sheet with the strong biasing force, so there is a risk of deformation that the side surface of the rolled sheet is dented.
As described above, in the conventional support structure for a rolled sheet, in order to prevent the rolled sheet from falling off, it is required to set the pressing force of the pair of support members to the large value, so there arise the several problems described above.